1. Field of the Invention
This invention relates to a monitor apparatus and method adapted for use with industrial-type voltage regulators and more particularly to a novel and highly effective monitor apparatus and method for efficiently keeping track of the tap position of an AC voltage regulator as it changes and maintaining a record of the tap position extremes between resets, thereby elevating standards of economy, maintenance, safety, and system performance analysis.
2. Description of the Prior Art
In service, a voltage regulator is supplied with an input voltage and in response thereto produces an output voltage. The purpose of a voltage regulator is to produce an output voltage that is well regulated: i.e., substantially constant at some predetermined target level, despite fluctuations in the input voltage and load from their normal values. An AC voltage regulator for industrial use typically comprises an autotransformer having a number of spaced-apart output terminals and performs its regulatory function by adjusting the tap position (in other words, tapping the output terminals at a selected position) so that, for a given input voltage, the output is taken from whichever tap yields an output voltage closest to the target level.
The number of taps provided depends on the environment in which the voltage regulator is designed to operate and the fineness or resolution with which it is necessary to control the output voltage. One type of voltage regulator in common use has the equivalent of 33 taps. These taps can be thought of as consisting of a centrally positioned neutral tap, 16 taps on one side of the neutral tap respectively corresponding to excursions of the input voltage of increasing magnitude in one direction from normal, and 16 taps on the opposite side of neutral respectively corresponding to excursions of the input voltage of increasing magnitude in the opposite direction from normal. In practice, such a voltage regulator has a neutral tap plus first through eighth additional taps and a reversing switch. The tap changer can be placed on the neutral tap to yield an output voltage equal to the input voltage. With the reversing switch in the "raise" position, the tap changer can be placed on the neutral and first taps for a one-raise, entirely on the first tap for a two-raise, on the first and second taps for a three-raise, entirely on the second tap for a four-raise, and so on until the tap changer is entirely on the eighth tap for a sixteen-raise. With the reversing switch in the "lower" position to reverse the current through the coil, the tap changer can be moved in the same way over the same taps to obtain any lower position ranging from a one-lower to a sixteen-lower.
The dynamic range at the input side is typically the normal input voltage plus or minus 10%. When the input voltage is at its normal value, the voltage regulator tap position is normally in neutral and the output voltage of the voltage regulator is equal to the input voltage.
Operators of large industrial electrical installations employing voltage regulators with tap changers need information about voltage regulator tap position because of its bearing on economy of operation, maintenance, safety, and system performance analysis.
Consider the matter of economy of operation. Sometimes, because of poor performance of a voltage regulator, power is supplied at a voltage which, although not so high as to damage the electrical components that receive power from the voltage regulator, is higher than the voltage required. In such a case, more power is delivered than is necessary, and the excess power is wasted. In a large industrial application, the waste can be quite substantial.
From the standpoint of maintenance and safety, in certain circumstances it is necessary to move the voltage regulator quickly and reliably to its neutral position. It is essential that the voltage regulator tap position be in neutral whenever the voltage regulator is placed in or removed from service. Information about current tap position is necessary to accomplish this.
From the standpoint of system performance analysis, a record of the successive active tap positions of a voltage regulator is a useful measure of the range and frequency of input voltage excursions and load changes, which are related respectively to the performance of the power supply to the voltage regulator and the performance of the system to which the voltage regulator supplies power.
Various kinds of apparatus have been developed in the past for determining the tap position of a voltage regulator. These prior developments have culminated in the standard electromechanical tap position indicator, which is physically attached to the tap changer mechanism, a mechanical device that changes the tap position by physically moving from tap to tap. The attached electromechanical tap position indicator moves with the tap changer mechanism and displays the tap position on a dial or in some other conventional manner.
The standard, conventional electromechanical meter has a number of drawbacks. For one, it has costly moving parts that wear out and is inherently less reliable and more expensive than one would wish. Moreover, it produces only a local meter indication, which can be read by an operator only by going to the site of the meter. While of course any meter reading can be converted into a signal that can be transmitted to a remote location for reading or to a centrally located computer for processing, such conversion requires an "add-on" device that increases the cost of the basic electromechanical meter.
Other prior art relating to the monitoring or determination of the tap position of a tap changer is found in U.S. Pat. Nos. 4,419,619, 4,612,617 and 5,119,012. The devices shown in these patents all have various drawbacks, including relative complexity and a failure to provide certain information or a failure to provide information in a form desired by operators of large industrial installations incorporating voltage regulators.